NAME¶
seccure - SECCURE Elliptic Curve Crypto Utility for Reliable Encryption
SYNOPSIS¶
seccure-key [-c curve] [-F pwfile] [-d] [-v]
[-q]
seccure-encrypt [-m
maclen] [-c curve] [-i
infile ] [-o outfile] [-v] [-q]
key
seccure-decrypt [-m
maclen] [-c curve] [-i
infile ] [-o outfile] [-F pwfile]
[-d] [-v] [-q]
seccure-sign [-f] [-b] [-a] [-c
curve] [-s sigfile] [-i
infile] [-o outfile] [-F pwfile]
[-d] [-v] [-q]
seccure-verify [-f] [-b] [-a] [-c
curve] [-s sigfile]
[-i infile] [-o outfile] [-v] [-q]
key [sig]
seccure-signcrypt [-c
sig_curve [-c enc_curve]] [-i
infile] [-o outfile] [-F pwfile]
[-d] [-v] [-q] key
seccure-veridec [-c
enc_curve [-c sig_curve]] [-i
infile] [-o outfile] [-F pwfile]
[-d] [-v] [-q] key
seccure-dh [-c
curve] [-v] [-q]
DESCRIPTION¶
The
seccure toolset implements a selection of asymmetric algorithms based
on elliptic curve cryptography (ECC). In particular it offers public key
encryption / decryption, signature generation / verification and basic key
establishment.
ECC schemes offer a much better key size to security ratio than classical
systems (RSA, DSA). Keys are short enough to make direct specification of keys
on the command line possible (sometimes this is more convenient than the
management of PGP-like key rings).
seccure builds on this feature and
therefore is the tool of choice whenever lightweight but nevertheless strong
asymmetric cryptography -- independent of key servers, revocation
certificates, the Web of Trust or even configuration files -- is required.
COMMANDS¶
seccure-key: Prompt for a passphrase and calculate the corresponding
public key.
seccure-encrypt: Encrypt a message with public key
key.
seccure-decrypt: Prompt for a passphrase and decrypt a
seccure-encrypted message.
seccure-sign: Prompt for a passphrase and digitally sign a message.
seccure-verify: Verify signature
sig with public key
key.
seccure-signcrypt: Sign a message first, encrypt it subsequently (in
-b -a and
-m 0 mode, respectively). This is basically a shortcut
for two separate
seccure invocations.
seccure-veridec: Counterpart to signcryption.
seccure-dh: Perform a Diffie-Hellman key exchange.
OPTIONS¶
- -c curve
- Use elliptic curve curve. Available are: secp112r1,
secp128r1, secp160r1, secp192r1/nistp192,
secp224r1/nistp224, secp256r1/nistp256,
secp384r1/nistp384 and secp521r1/nistp521. The curve name
may be abbreviated by any non-ambiguous substring (for instance it is
suggested to specify p224 for the secp224r1/nistp224 curve).
The default curve is p160, which provides reasonable security for
everyday use. (See also HOW TO CHOOSE THE CURVE.)
Note: If a public key is given on the command line seccure can
determine the corresponding curve on its own. It's then unnecessary to
specify the curve explicitly.
- -F pwfile
- Don't prompt for a passphrase; instead, take the first text line of
pwfile.
- -m maclen
- Set the MAC length to maclen bits. Only multiples of 8 in the range
from 0 to 256 are allowed. The default MAC length is 80 bits, which
provides a reasonable level of integrity protection for everyday use.
- -i infile
- Read from infile instead of STDIN.
- -o outfile
- Write to outfile instead of STDOUT.
- -s sigfile
- For seccure-sign: Write signature to sigfile instead of
STDERR.
For seccure-verify: Read signature from sigfile instead of
using sig.
- -f
- Filter mode: Copy all data read from STDIN verbatim to STDOUT (eventually
attaching or detaching a signature in -a mode).
- -b
- Binary mode: Read/write signatures as binary strings. This leads to very
compact signatures.
- -a
- Append mode:
For seccure-sign: Append signature to the end of the document. This
enforces -f mode.
For seccure-verify: Detach signature from the end of the
document.
- -d
- Double prompt mode: When reading a passphrase from the console: prompt
twice and assure the phrases are the same.
- -v
- Verbose mode: Print some extra information.
- -q
- Quiet mode: Disable all unnecessary output.
EXIT STATUS¶
All commands in the
seccure software suite exit with a status of zero if
the desired operation could be completed successfully. Any error leads to a
nonzero exit code.
EXAMPLE¶
Given the passphrase 'seccure is secure', run
seccure-key
to determine the corresponding public key (which is '2@DupCaCKykHBe-QHpAP%d%B['
on curve
p160).
To encrypt the file 'document.msg' with that key run
seccure-encrypt -i document.msg -o document.enc
'2@DupCaCKykHBe-QHpAP%d%B['
The message can be recovered with
seccure-decrypt -i document.enc
To sign the file run
seccure-sign -i document.msg -s document.sig
and enter the passphrase. The signature is stored in 'document.sig' and can be
verified with
seccure-verify -i document.msg -s document.sig
'2@DupCaCKykHBe-QHpAP%d%B['
KEY ESTABLISHMENT¶
seccure-dh performs an interactive Diffie-Hellman key exchange. Two
instances have to be run in parallel; the token generated by the first
instance is the input for the second one and vice versa. The output consists
of two shared keys: it is guaranteed that no attacker can ever find out the
established key as soon as the two parties can confirm that both have the same
verification key. The authentic comparision of the verification keys can, for
example, be realized via signed messages or via telephone (using 'voice
authentication').
HOW TO CHOOSE THE CURVE¶
The number in the name of a curve measures its security level. Rule of thumb:
the workload to 'break' a k-bit curve is 2^(k/2) approximately (example: it
takes about 2^112 steps to break
secp224r1). If the 80 bit security of
the default curve doesn't seem sufficient, choosing a stronger curve (
p192 and upwards) may, of course, be considered. But the suggestion
remains:
p160 offers reasonable security for everyday use.
Warning: the curves
p112 and
p128 do not satisfy demands
for long-time security.
ALGORITHMS¶
seccure uses derivated versions of ECIES (Elliptic Curve Integrated
Encryption Scheme), ECDSA (Elliptic Curve Digital Signature Algorithm) and
ECDH (Elliptic Curve Diffie-Hellman) as encryption, signature and key
establishment scheme, respectively. For the symmetric parts (bulk encryption,
hashing, key derivation, HMAC calculation)
seccure builds on AES256 (in
CTR mode), SHA256 and SHA512. To my best knowledge no part of
seccure
is covered by patents. See the file PATENTS for an explicit patent statement.
AUTHOR¶
This software (v0.4) was written by B. Poettering (seccure AT
point-at-infinity.org) in 2009. It is released under the terms of the GNU
General Public License (GPL). Find the latest version of
seccure on the
project's homepage:
http://point-at-infinity.org/seccure/.